Comparison of three methods of glomerular filtration rate measurement with and without captopril pretreatment in groups of patients with left ventricular dysfunction

Methods of glomerular filtration rate measurement by 51Cr EDTA elimination, inulin clearance and creatinine clearance were compared with and without captopril pretreatment in 10 chronic heart failure patients and in 20 patients after transmural myocardial infarction. Strong intermethod correlations were found in chronic heart failure patients (EDTA: inulin r = 0.87; EDTA: creatinine r = 0.84; inulin: creatinine r = 0.9; all P less than 0.00001). Despite this, substantial absolute differences were observed in results obtained by different techniques. In particular, creatinine clearance significantly overestimated both 51Cr EDTA (18.0 +/- 18.4 ml.min-1, mean difference +/- SD, P less than 0.001) and inulin clearance (26.8 +/- 17.0 ml.min-1, P less than 0.001). The slight reduction in 51Cr EDTA elimination on captopril versus placebo (-8.3 +/- 9.2 ml.min-1, P less than 0.05) was related to a similar treatment difference in inulin clearance (r = 0.67, p = 0.03), but changes observed by either method were unrelated to captopril-induced changes in creatinine clearance. Thus, creatinine clearance is an unsatisfactory means of assessing the effect of angiotensin converting enzyme inhibition on glomerular filtration rate in chronic heart failure. In the post-myocardial infarction group, correlations between methods were poorer (EDTA: inulin r = 0.79; EDTA: creatinine r = 0.76; inulin: creatinine r = 0.67). In this group no significant effect of captopril on glomerular filtration rate was detected by any technique. As compared to the chronic heart failure patients, the weaker relationship between techniques post-myocardial infarction may be related to interference by thrombolytic or aspirin treatment.